I had a similar/same experience. Booted S4-Sprint up, listing a Samsung download about 90% complete and downloading. This continued and I investigated, since I didn't request any updates and why was this download not completing? Couldn't figure out what was downloading. Booted up again and this incomplete download was gone. I don't have Knox or automatic security downloads. Looked to me like the Knox messages after the previous OS and the removal of the problem with kitkat. ie a screwup.